Pyrolysis Kinetic Study and Reaction Mechanism of Epoxy Glass Fiber Reinforced Plastic by Thermogravimetric Analyzer (TG) and TG-FTIR (Fourier-Transform Infrared) Techniques

Hybrid hemp/glass fiber reinforced high-temperature shape memory photopolymer with mechanical and flame-retardant analysis

Cultivated natural fibers have a huge possibility for green and sustainable reinforcement for polymers, but their limited load-bearing ability and flammability prevent them from wide applications in composites. According to the beam theory, normal stress is the maximum at the outermost layers but zero at the mid-plane under bending (with (non)linear strain distribution). Shear stress is the maximum at the mid-plane but manageable for most polymers. Accordingly, a laminated composite made of hybrid fiber-reinforced shape memory photopolymer was developed, incorporating strong synthetic glass fibers over a weak core of natural hemp fibers. Even with a significant proportion of natural hemp fibers, the mechanical properties of the hybrid composites were close to those reinforced solely with glass fibers. The composites exhibited good shape memory properties, with at least 52% shape fixity ratio and 71% shape recovery ratio, and 24 MPa recovery stress. After 40 s burning, a hybrid composite still maintained 83.53% of its load carrying capacity. Therefore, in addition to largely maintaining the load carrying capacity through the hybrid reinforcement design, the use of shape memory photopolymer endowed a couple of new functionalities to the composites: the plastically deformed laminated composite beam can largely return to its original shape due to the shape memory effect of the polymer matrix, and the flame retardancy of the polymer matrix makes the flammable hemp fiber survive the fire hazard. The findings of this study present exciting prospects for utilizing low-strength and flammable natural fibers in multifunctional load-bearing composites that possess both flame retardancy and shape memory properties.

Isoconversional thermal decomposition reaction kinetics of oil palm trunk and rubberwood sawdust for thermochemical conversion processes

Biomass as a raw material has profound implications for thermal conversion processes. It is important to study the relationship between kinetic modeling to depict significant importance in thermal processing by estimating volatile yield and reaction performance during biomass decomposition. This work aimed to determine the thermal decomposition reaction kinetics of non-woody (oil palm trunk (OPT)) and woody (rubberwood sawdust (RWS)) biomass. Devolatilization of biomass is determined by the thermogravimetric analysis (TGA) at three different heating rates (10, 20, and 30 °C/min) using nitrogen as inert gas. The kinetic analysis used isoconversion models of Friedman, Ozawa-Flynn-Wall (OFW), and Kissinger-Akahira-Sunose (KAS). The activation energy varied from 218.4 to 303.8 kJ/mol (Friedman), 235.9 to 299.1 kJ/mol (OFW), and 235.8 to 298.9 kJ/mol (KAS) for OPT; and 199.7 to 228.1 kJ/mol (Friedman), 210.6 to 225.6 kJ/mol (OFW), and 210.7 to 225.2 kJ/mol (KAS) for RWS. The kinetic analysis indicated that RWS and OPT had diverse reaction kinetics, which depend on the reaction rate and order of the reaction. Experimental and theoretical conversion data agreed reasonably well, indicating that these results can be used for future OPT and RWS process modeling. Consistency of results is validated using GC-MS equipped with a pyrolyzer.

In-situ pyrolysis kinetic analysis and fixed-bed pyrolysis behavior of ex-service wind turbine blades

After the peak of rapid wind power development, a large amount of wind turbine blades reach/exceed their service life due to aging or damage. These ex-service wind turbine blades (EWTB) will increase the issue of its high-efficient utilization in the future decades. Among several treatment methods, pyrolysis has been considered as a promising solution to separate inorganic fiberglass and make organic epoxy resin (OER) high-value-added converted. However, the pyrolysis mechanism, chemical composition, and fiberglass separation of EWTB have not been deeply studied. In this paper, the synthetic model compound of epoxy resin was firstly used to investigate the thermal weight loss and pyrolysis kinetics, the thermal weight loss temperature range of which was 300 ∼ 480 °C. The apparent activation energy was minimum when the conversion rate was 0.6, and the pyrolysis mechanism was determined by the Coats-Redfern method as a diffusion control. On this basis, a lab-scale fixed-bed was conducted to study fast-heating pyrolysis characteristics of EWTB. It could be analyzed that the chemicals in the pyrolytic liquid were a series of phenolics with methyl and vinyl substituted benzene rings (e.g., bisphenol A, p-isopropenyl phenol, and phenol). Bisphenol A presented a relatively high selectivity of 51.02%, which could be recycled as the main raw material for the synthesis of epoxy resins. Furthermore, clean fiberglass could be separated by combusting the residual carbon in pyrolytic solids. These results might be useful for achieving the separation and resource utilization of organic and inorganic components of EWTB.

Comparative Thermal Degradation Behaviors and Kinetic Mechanisms of Typical Hardwood and Softwood in Oxygenous Atmosphere

In order to utilize woody biomass effectively for bioenergy and chemical feedstocks, the comparative thermal degradation behaviors and kinetic mechanisms of typical hardwood (beech wood) and softwood (camphorwood) were studied at various heating rates in air. The Kissinger-Akahira-Sunose approach combined with the Coats-Redfern approach was employed to estimate the kinetic triplet. Softwood degradation began and ended at lower temperatures than hardwood. Compared with softwood, the maximal reaction rate of hardwood was greater and occurred in the higher temperature region. Two decomposition regions were determined by the variation of activation energy, and the dividing point was α = 0.6 and α = 0.65 for hardwood and softwood, respectively. Moreover, the average activation energy of hardwood was larger than that of softwood during the whole decomposition process. The thermal degradation process occurring in region 1 was dominated by the Avrami-Erofeev and 3D diffusion models for hardwood and softwood, respectively. Furthermore, the kinetic modeling results showed good consistency between the experimental and simulated curves under 5, 15, 20, and 40 K/min. It is noted that the thermogravimetric experimental profile under 20 K/min was not used for estimating the kinetic triplet. Besides, the combustion performance of hardwood is superior to softwood under the same external conditions (heating rate and atmosphere).

Pyrolysis Kinetic Behaviour of Glass Fibre-Reinforced Epoxy Resin Composites Using Linear and Nonlinear Isoconversional Methods

Due to the increasing demand for glass fibre-reinforced epoxy resin composites (GFRC), huge amounts of GFRC waste are produced annually in different sizes and shapes, which may affect its thermal and chemical decomposition using pyrolysis technology. In this context, this research aims to study the effect of mechanical pre-treatment on the pyrolysis behaviour of GFRC and its pyrolysis kinetic. The experiments were started with the fabrication of GFRC panels using the vacuum-assisted resin transfer method followed by crushing the prepared panels using ball milling, thus preparing the milled GFRC with uniform shape and size. The elemental, proximate, and morphology properties of the panels and milled GFRC were studied. The thermal and chemical decomposition of the milled GFRC was studied using thermogravimetric coupled with Fourier-transform infrared spectroscopy (TG-FTIR) at different heating rates. Meanwhile, the volatile products were examined using TG coupled with gas chromatography-mass spectrometry (GC-MS). The TG-FTIR and TG-GC-MS experiments were performed separately. Linear (Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO), and Friedman) and nonlinear (Vyazovkin and Cai) isoconversional methods were used to determine the pyrolysis kinetic of the milled GFRC based on thermogravimetry and differential thermal gravimetry (TG/DTG). In addition, the TG/DTG data of the milled GFRC were fitting using the distributed activation energy model and the independent parallel reactions kinetic model. The TG results showed that GFRC can decompose in three stages, and the main decomposition is located in the range 256-500 °C. On the other hand, aromatic benzene and a C-H bond were the major functional groups in the released volatile components in FTIR spectra, while phenol (27%), phenol,4-(1-methylethyl) (40%), and p-isopropenylphenol (34%) were the major compounds in GC-MS analysis. Whereas, the kinetic results showed that both isoconversional methods can be used to determine activation energies, which were estimated 165 KJ/mol (KAS), 193 KJ/mol (FWO), 180 KJ/mol (Friedman), 177 KJ/mol (Vyazovkin), and 174 KJ/mol (Cai).

Thermodynamic and Kinetic Characteristics of Combustion of Discrete Polymethyl Methacrylate Plates with Different Spacings in Concave Building Facades

Polymethyl methacrylate plates are widely applied to buildings, producing significant fire hazards. It lacks a theoretical basis for the fire risk assessment of polymethyl methacrylate in concave building facades. Therefore, experimental methods are used to investigate combustion characteristics of discrete polymethyl methacrylate plates in a concave building facade. Influences of fuel coverage and structure factor are investigated, which is scant in previous works. When structure factor is invariable, average flame height increases first and then decreases as fuel coverage increases, and the turning point is between 0.64 and 0.76. In total, three different patterns of pyrolysis front propagation are first observed for different fuel coverages. Flame spread rate first increases and then decreases as fuel coverage rises, and the turning point is also between 0.64 and 0.76. When fuel coverage is invariable, the flame spread rate first increases and then decreases with increasing structure factor, and the turning point is 1.2. A model for predicting the flame spread rate of discrete polymethyl methacrylate is also developed. The predicted values are consistent with experimental results. Fuel spread rate of discrete polymethyl methacrylate rises as the fuel coverage increases. The above results are beneficial for thermal hazard evaluation and fire safety design of polymethyl methacrylate used in buildings.